Behavioral deficits due to carbon monoxide (CO) exposure are investigated using the operant conditioning situation. Rats and squirrel monkeys are subjects. The procedures for presentation of CO uses bottled CO injected into an air stream drawn through the experimental chamber. Before and after the chamber, a small amount of the stream is diverted to an analyzer. Present studies are investigating "chronic" exposure reaction (24 hours to 2 weeks). Complex schedules of reinforcement such as counting schedules, progressive ration and differential reinforcement of low rates have produced deficits related to concentration of CO, duration of exposure to CO, and rate of change of percent carboxyhemoglobin (COHb) produced by CO exposure. COHb determinations have been made for the Long-Evans hooded rats at CO concentrations from 250 to 1000 ppm and for exposure durations of 15 to 240 minutes. A study of contrast sensitivity in the squirrel monkey under CO has been completed and procedures for chronic exposure to CO have been used repeating all of the procedures mentioned above. Speculations have been offered as to why specific performances are particularly sensitive to CO exposure. BIBLIOGRAPHIC REFERENCES: Ator, N.A., Merigan, W.H., and McIntire, R.W. The effects of brief exposures to carbon monoxide on temporally differentiated responding. Environmental Research, 1976, in press. Smith, M.D., Merigan, W.H., and McIntire, R.W. Effects of carbon monoxide exposure counting accuracy in the rat. Pharmacology, Biochemistry and Behavior, 1976, in press.